The present invention relates to a device for removing clearance or tappet clearance in a valve mechanism used for an internal combustion engine, particularly a horizontal opposed type internal combustion engine.
A tappet clearance removing device has heretofore been known, for example, in Japanese patent Laid-Open Nos. 41613/84 and 2266217/84 wherein a cutout portion is formed in an eccentric cam which supports a rocker arm, and a plunger of a hydraulic adjuster is brought into pressure contact with this cutout portion to exert a rotating force to the eccentric cam, thereby bringing the rocker arm into pressure contact with a valve operating cam and an intake or exhaust valve stem.
In the above prior art, since the pressure bearing surface of the cutout portion of the eccentric cam is so small in size and working radius that upon pressure contact therewith of the plunger of the hydraulic adjuster to apply a required torque thereto, a high surface pressure is developed, which is likely to cause friction. Further, in order for the plunger to act in a tangential direction, it has been necessary to pay special attention to the shape of the cutout portion and the mounting posture of the hydraulic adjuster.
The present invention has overcome the above-mentioned problems. More particularly, in a rocker arm clearance removing device wherein torque is applied by a hydraulic adjuster to an eccentric cam which supports a rocker arm and the resulting rotation of the eccentric cam causes the rocker arm to come into pressure contact with a valve operating cam and an intake valve or an exhaust valve, a first aspect of the present invention is characterized in that the eccentric cam is supported by a rocker arm shaft extending through an eccentric position of the cam; a substantially radially extending, pressure bearing arm is projected from an end portion of the eccentric cam so as to form a pressure bearing surface which faces in a rotating direction of the arm; and the hydraulic adjuster, which has a pressurizing surface for abutment with the pressure bearing surface, is disposed nearly perpendicularly to the pressure bearing surface.
The pressure bearing arm of the eccentric cam is pushed by the plunger of the hydraulic adjuster and thereby pivots about the rocker arm shaft to move the rocker amr. At this time, a large torque is developed even at a small urging force of the plunger because the working radius of the pressure bearing surface of the pressure bearing arm is larger than the radius of the eccentric cam. Additionally, since the hydraulic adjuster operates approximately perpendicularly to the pressure bearing surface, there will not be developed a sideways component of force, thus preventing wear of the hydraulic adjuster.
A second aspect of the present invention resides in a stopper mechanism which restricts the posture of the eccentric cam. More particularly, in a rocker arm device in an internal combustion engine wherein torque is applied by a hydraulic adjuster to an eccentric cam which supports a rocker arm and the resulting rotation of the eccentric cam causes the rocker arm to come into pressure contact with a valve operating cam and an intake valve or an exhaust valve, the second aspect of the present invention is characterized in that radially extending pressure bearing arm and engaging piece are projectingly provided on an end portion of the eccentric cam in a circumferentially spaced manner; an arm stopper is provided on an opening side of a case of the hydraulic adjuster to prevent the pressure bearing arm from entering the interior of the said case; and a swivel stop means adapted to engage the said engaging piece in a rotational position beyond a preset operational range of the eccentric cam to stop the cam is provided at a side part of the case.
Under the above construction, even when the pressure bearing arm turns to the hydraulic adjuster side, it will be stopped by the arm stopper so it will not strike the inner or end surface of the case. The rotation of the eccentric cam in the opposite direction is restricted by abutment of the engaging piece of the cam with the swivel stop provided on the case side.